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<h1>Module <a href="type_Genlex.html">Genlex</a></h1>

<pre><span id="MODULEGenlex"><span class="keyword">module</span> Genlex</span>: <code class="code"><span class="keyword">sig</span></code> <a href="Genlex.html">..</a> <code class="code"><span class="keyword">end</span></code></pre><div class="info module top">
<div class="info-desc">
<p>A generic lexical analyzer.</p>

<p>This module implements a simple 'standard' lexical analyzer, presented
   as a function from character streams to token streams. It implements
   roughly the lexical conventions of OCaml, but is parameterized by the
   set of keywords of your language.</p>

<p>Example: a lexer suitable for a desk calculator is obtained by</p>
<pre class="codepre"><code class="code">     <span class="keyword">let</span> lexer = make_lexer [<span class="string">"+"</span>;<span class="string">"-"</span>;<span class="string">"*"</span>;<span class="string">"/"</span>;<span class="string">"let"</span>;<span class="string">"="</span>; <span class="string">"("</span>; <span class="string">")"</span>]  </code></pre>
<p>The associated parser would be a function from <code class="code">token&nbsp;stream</code>
   to, for instance, <code class="code">int</code>, and would have rules such as:</p>

<pre class="codepre"><code class="code">           <span class="keyword">let</span> <span class="keyword">rec</span> parse_expr = <span class="keyword">parser</span>
             <span class="keywordsign">|</span> [&lt; n1 = parse_atom; n2 = parse_remainder n1 &gt;] <span class="keywordsign">-&gt;</span> n2
           <span class="keyword">and</span> parse_atom = <span class="keyword">parser</span>
             <span class="keywordsign">|</span> [&lt; <span class="keywordsign">'</span><span class="constructor">Int</span> n &gt;] <span class="keywordsign">-&gt;</span> n
             <span class="keywordsign">|</span> [&lt; <span class="keywordsign">'</span><span class="constructor">Kwd</span> <span class="string">"("</span>; n = parse_expr; <span class="keywordsign">'</span><span class="constructor">Kwd</span> <span class="string">")"</span> &gt;] <span class="keywordsign">-&gt;</span> n
           <span class="keyword">and</span> parse_remainder n1 = <span class="keyword">parser</span>
             <span class="keywordsign">|</span> [&lt; <span class="keywordsign">'</span><span class="constructor">Kwd</span> <span class="string">"+"</span>; n2 = parse_expr &gt;] <span class="keywordsign">-&gt;</span> n1+n2
             <span class="keywordsign">|</span> [&lt; &gt;] <span class="keywordsign">-&gt;</span> n1
   </code></pre>
<p>One should notice that the use of the <code class="code"><span class="keyword">parser</span></code> keyword and associated
   notation for streams are only available through camlp4 extensions. This
   means that one has to preprocess its sources <i>e. g.</i> by using the
   <code class="code"><span class="string">"-pp"</span></code> command-line switch of the compilers.</p>
</div>
</div>
<hr width="100%">

<pre><code><span id="TYPEtoken"><span class="keyword">type</span> <code class="type"></code>token</span> = </code></pre><table class="typetable">
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTtoken.Kwd"><span class="constructor">Kwd</span></span> <span class="keyword">of</span> <code class="type">string</code></code></td>

</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTtoken.Ident"><span class="constructor">Ident</span></span> <span class="keyword">of</span> <code class="type">string</code></code></td>

</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTtoken.Int"><span class="constructor">Int</span></span> <span class="keyword">of</span> <code class="type">int</code></code></td>

</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTtoken.Float"><span class="constructor">Float</span></span> <span class="keyword">of</span> <code class="type">float</code></code></td>

</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTtoken.String"><span class="constructor">String</span></span> <span class="keyword">of</span> <code class="type">string</code></code></td>

</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTtoken.Char"><span class="constructor">Char</span></span> <span class="keyword">of</span> <code class="type">char</code></code></td>

</tr></table>

<div class="info ">
<div class="info-desc">
<p>The type of tokens. The lexical classes are: <code class="code"><span class="constructor">Int</span></code> and <code class="code"><span class="constructor">Float</span></code>
   for integer and floating-point numbers; <code class="code"><span class="constructor">String</span></code> for
   string literals, enclosed in double quotes; <code class="code"><span class="constructor">Char</span></code> for
   character literals, enclosed in single quotes; <code class="code"><span class="constructor">Ident</span></code> for
   identifiers (either sequences of letters, digits, underscores
   and quotes, or sequences of 'operator characters' such as
   <code class="code">+</code>, <code class="code">*</code>, etc); and <code class="code"><span class="constructor">Kwd</span></code> for keywords (either identifiers or
   single 'special characters' such as <code class="code">(</code>, <code class="code">}</code>, etc).</p>
</div>
</div>


<pre><span id="VALmake_lexer"><span class="keyword">val</span> make_lexer</span> : <code class="type">string list -> char <a href="Stream.html#TYPEt">Stream.t</a> -> <a href="Genlex.html#TYPEtoken">token</a> <a href="Stream.html#TYPEt">Stream.t</a></code></pre><div class="info ">
<div class="info-desc">
<p>Construct the lexer function. The first argument is the list of
   keywords. An identifier <code class="code">s</code> is returned as <code class="code"><span class="constructor">Kwd</span>&nbsp;s</code> if <code class="code">s</code>
   belongs to this list, and as <code class="code"><span class="constructor">Ident</span>&nbsp;s</code> otherwise.
   A special character <code class="code">s</code> is returned as <code class="code"><span class="constructor">Kwd</span>&nbsp;s</code> if <code class="code">s</code>
   belongs to this list, and cause a lexical error (exception
   <a href="Stream.html#EXCEPTIONError"><code class="code"><span class="constructor">Stream</span>.<span class="constructor">Error</span></code></a> with the offending lexeme as its parameter) otherwise.
   Blanks and newlines are skipped. Comments delimited by <code class="code">(*</code> and <code class="code">*)</code>
   are skipped as well, and can be nested. A <a href="Stream.html#EXCEPTIONFailure"><code class="code"><span class="constructor">Stream</span>.<span class="constructor">Failure</span></code></a> exception
   is raised if end of stream is unexpectedly reached.</p>
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